@media doesn't disable header Ad on Mobile site

[giorgino]

Hi all. Weird issue.

I set up the advertising position "container header" with a 729x90 banner into.
The code is

Code:

<div class="ad_header" id="87439-1">
         [ad code]
</div>

and the CSS code I inserted in extra.css is

CSS:

@media (max-width: 960px) {
    .ad_header {
        display: none;
    }
}

It works as expected in the PC browser window, but not on mobile version where this is the output



Can you please help with this?

Thanks

Giorgio